The mouse formin gene when mutated gives rise to a recessively-inherited dysmorphic syndrome consisting of oligosyndactyly with synostosis of the long bones of the limbs and renal agenesis/dysgenesis. Several protein isoforms are encoded by this gene. Six mutant alleles have been described. These mutants exhibit a completely penetrant limb phenotype and incompletely penetrant renal agenesis (20-98%). An isoform-specific null exhibits only the renal phenotype. We found that the variable pentrance is allele-specific. Given the complexity of the gene structure and the mutant phenotype, this gene!s function will be studied by generating a complete deletion.